<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

</body>
<script>
    // 输入框
    let age = parseInt(prompt('你现在多少岁了？'));
    // 弹出框
    alert(`据我估计，五年后，你可能${age + 5}岁了`);
</script>

</html>